1. Field of Invention
The present invention relates to a method for fabricating an Alxe2x80x94Sixe2x80x94containing alloy line. More particularly, the present invention relates to forming a conductive line on a substrate.
2. Description of Related Art
When the integration of a semiconductor device increases, there is not enough surface area on a chip for interconnect formation. If the demand for interconnects, which are adapted to connect the semiconductor devices, is to be met, multilevel interconnects are a necessary element for the manufacture of the metal oxide semiconductor. The multilevel interconnect is always formed after the fabrication of the semiconductor device is complete and a connecting system is established for transporting electric message thereon.
Aluminum is a very important conductive material in the development of integrated circuit devices. Due to the low resistivity thereof, aluminum is suitable for decreasing the RC delay time and increasing the switching frequency. At the same time, there are some disadvantages in using aluminum as a conductive material, such as spiking and poor electromigration resistance. In order to overcome the disadvantages of the aluminum, appropriate amounts of silicon and copper are added in aluminum and aluminum-silicon-copper (Alxe2x80x94Sixe2x80x94containing) alloy is formed. Typically, the silicon content in the alloy is about 1% and the copper content in the alloy is about 0.5% to 4%.
Reference is made to FIG. 1, which illustrates a schematic, cross-sectional diagram showing an Alxe2x80x94Sixe2x80x94containing alloy conductive line as disclosed in the prior art. A wafer 100 with devices formed thereon is provided. A conductive layer 102 made of titanium, titanium silicide or tungsten titanium alloy is formed on the wafer 100 by deposition to lower the sheet resistance between conductive line and plugs (not shown in the figure). A conductive layer 104 made of titanium nitride or a tungsten titanium alloy film is deposited as a barrier layer and an adhesion layer. The main portion of the conductive line is an aluminum-copper-silicon film 106. Finally, a titanium nitride layer 108 is deposited on the aluminum-copper-silicon film 106 as an anti-reflection layer. The temperature for depositing titanium nitride is typically between about 100xc2x0 C. and 200xc2x0 C., but it also can be formed at room temperature. The aluminum-copper-silicon film 106 is formed by high temperature sputtering between about 300xc2x0 C. and 500xc2x0 C. and a subsequent reflow process at about 450xc2x0 C. to 500xc2x0 C. to increase the step coverage of the aluminum alloy.
Reference is made to FIG. 2, a schematic, which illustrates a cross-sectional diagram showing the silicon separating out in the Alxe2x80x94Sixe2x80x94containing alloy conductive line. The solubility of the silicon in aluminum decreases directly with temperature. In other words, a higher temperature means a greater solubility of the silicon in aluminum. Reference is made to FIG. 6, FIG. 6 is printed from M. Hansen and A. Anderko, xe2x80x9cConstitution of Binary Alloys,xe2x80x9d McGraw-Hill, New York, 1958, which is a phase diagram of the silicon-containing percentage of Alxe2x80x94Si alloy at different temperatures. From the enlarged diagram positioned at the upper left corner, the solubility of the silicon in aluminum at 577xc2x0 C. is about 1.5%, but when the temperature is lowered below 440xc2x0 C., the solubility of the silicon decreases very quickly. If the Alxe2x80x94Si alloy cools down slowly, it will follow the curve of solid solubility and the ultra-saturated silicon in the Alxe2x80x94Si alloy will separate out. The grain boundary and the interface boundary of the aluminum alloy is the result of the defects of the crystal, the energy barrier for nucleation is smaller. Therefore, in the annealing process, the over-saturated silicon separates out. The silicon crystal 200 nucleates and grows within.
Reference is made to FIG. 3, which illustrates a cross-sectional diagram showing an Alxe2x80x94Sixe2x80x94containing alloy conductive line having silicon residue. The silicon crystals 200 are not removed in the etching process for defining the conductive lines and become residues on the surface of the substrate. Silicon crystal 200 between two conductive lines 204 forms a bridge and thus a short occurs therebetween. Further, a poorer electromigration resistance of the aluminum is caused by the silicon crystal 200 at the grain boundary 202 of the aluminum crystal.
In accordance with the above background of the invention, the conventional manufacturing method for forming an Alxe2x80x94Sixe2x80x94containing alloy conductive line has disadvantages. The silicon residue between the two Alxe2x80x94Sixe2x80x94containing alloy conductive lines causes these two lines to short and the yield decreases accordingly. Therefore, it is necessary find a process for manufacturing an Alxe2x80x94Sixe2x80x94containing alloy conductive line that improves upon the conventional approaches. It is therefore an objective of the present invention to provide a method for fabricating an Alxe2x80x94Sixe2x80x94containing alloy conductive line, in which the annealing process after the high temperature deposition process or thermal flow process is modified so that no silicon residue exists.
It is another an objective of the present invention to provide a method for fabricating an Alxe2x80x94Sixe2x80x94containing alloy conductive line, in which the temperature (after the high temperature deposition process or the thermal flow process) is lowered faster and escapes from the curve of solid solubility of silicon and aluminum. The temperature decreases so fast that there is no suitable condition (temperature and time) for the over-saturated silicon to nucleate and grow.
It is still another objective of the present invention to provide a method for fabricating an Alxe2x80x94Sixe2x80x94containing alloy conductive line, in which the rapidly lowering temperature (after the high temperature deposition process or thermal flow process lead the Alxe2x80x94Sixe2x80x94containing alloy into a sub-stable state. Alxe2x80x94Sixe2x80x94containing alloy in the sub-stable state preserves the high-temperature solubility of aluminum in silicon, even at room temperature. Therefore, the silicon does not separate from the aluminum-containing alloy.
In accordance with the foregoing and other objectives of the present invention, a method for fabricating an Alxe2x80x94Sixe2x80x94containing alloy conductive line is provided. A film of titanium, titanium silicide or tungsten titanium alloy is formed by deposition to lower the sheet resistance. A titanium nitride or a tungsten titanium alloy film is deposited as a barrier layer and an adhesion layer. The main portion of the conductive line is an aluminum-copper-silicon film, which is formed by high temperature sputtering between about 300xc2x0 C. and 500xc2x0 C. Finally, titanium nitride is deposited as an anti-reflection layer. The temperature for depositing titanium nitride is typically between about 100xc2x0 C. and 200xc2x0 C., but it also can be formed at room temperature. Therefore, before the deposition of the titanium nitride, the wafer is cooled down rapidly to about 20xc2x0 C. or lower, followed by a titanium nitride deposition process. The time needed for cooling down the wafer is between about 1 second and 10 seconds.
In the conventional manufacturing method for forming an Alxe2x80x94Sixe2x80x94containing alloy conductive line, an aluminum-copper-silicon film is formed by high temperature sputtering between about 300xc2x0 C. and 500xc2x0 C. The wafer""s temperature is lowered to between about 100xc2x0 C. and 200xc2x0 C., followed by a titanium nitride deposition process. After this, the wafer""s temperature is cooled down to room temperature. These procedures are a slow cooling down process for Alxe2x80x94Sixe2x80x94containing alloy. The silicon separates out during the cooling down and titanium nitride deposition processes and the silicon nucleates and grows at the grain boundary of the aluminum and the interface boundary between the two films. For this reason, the method disclosed in this invention provides a rapid cooling down process, in which the temperature decreases so fast that there is no suitable condition for the over-saturated silicon to nucleate and grow.
Further-more, this invention provides another method for fabricating an Alxe2x80x94Sixe2x80x94containing alloy conductive line. A film of titanium, titanium silicide or tungsten titanium alloy is formed by deposition to decrease the sheet resistance as disclosed in the prior art. A titanium nitride or a tungsten titanium alloy film is deposited as a barrier layer and an adhesion layer. The main portion of the conductive line is an aluminum-copper-silicon film, which is formed by high temperature sputtering between about 300xc2x0 C. and 500xc2x0 C. The wafer""s temperature is lowered for depositing the titanium nitride but the temperature is lowered by no more than about 50xc2x0 C. That is to say the temperature for depositing titanium nitride is between about 250xc2x0 C. and 450xc2x0 C. Finally, the wafer is cooled rapidly to about 20xc2x0 C. or lower. The time needed for cooling the wafer is between about 1 second and 10 seconds. Similarly, the temperature decreases so fast that there is no suitable condition (temperature and time) for the over-saturated silicon to nucleate and grow.
It is to be understood that both the foregoing general description and the following detailed description are examples, only, and are intended to provide further explanation of the invention as claimed.